1. Field of the Invention
The present invention relates to a resin composite hose of curved shape including a resin layer that is disposed in the middle of multilayers, has a permeation resistance to a transported fuel and serves as a barrier layer, and a method for producing such a resin composite hose of curved shape.
2. Description of the Related Art
For application of a fluid transporting hose, for example, a fuel hose in a motor vehicle, a typical rubber hose made of a blend of acrylonitrile-butadiene rubber and polyvinyl chloride (NBR/PVC blend, NBR+PVC) or the like has been conventionally used. Such rubber hose has a high vibration-absorbability, easiness of assembly, and an excellent permeation resistance to a fuel (gasoline).
However, recently, in view of global environmental conservation, regulations on restriction of permeation of motor vehicle fuel has been tightened, and demand for fuel permeation resistance is expected to increase more and more in future.
As a countermeasure against that, developed and used is a resin composite hose including a resin layer that is laminated as an inner surface layer on an inner side of an outer rubber layer, has an excellent filet permeation resistance and serves as a barrier layer.
However, the resin layer as the barrier layer is hard since resin is a material harder than rubber. So, in a hose including the resin layer laminated on an inner side of the outer rubber layer to an extreme end thereof (an axial end of the hose), when the hose is fitted on a mating pipe, a sealing property becomes insufficient due to poor bonding between the mating pipe and the resin layer that defines an inner surface of the hose.
And, since the resin layer defining the inner surface of the hose is hard and has a large deformation resistance, a great force is required for fitting or slipping the hose on the mating pipe. This causes a problem that easiness of connection of the hose and the mating pipe is impaired.
For the purpose of solution of the problem, a hose as shown in FIG. 8 is disclosed in Patent Document 1 below.
In the Figure, reference numeral 200 indicates a resin composite hose, reference numeral 202 indicates an outer rubber layer, and reference numeral 204 is a resin layer that is laminated on an inner surface of the outer rubber layer 202 as a barrier layer.
In the resin composite hose 200, on an end portion thereof to be connected to a mating pipe 206 made of metal, the resin layer 204 is not laminated, and an inner surface of the outer rubber layer 202 is exposed so as to be fitted on the mating pipe 206 directly and elastically in contact relation.
And, in order to prevent a problem that a fuel flowing inside penetrates between the exposed inner surface of the outer rubber layer 202 and the mating pipe 206, and permeates outside through the end portion of the outer rubber layer 202 on which the resin layer 204 is not laminated, in the resin composite hose 200, an annular grooved portion 208 is formed in an end portion of the resin layer 204, a ring-shaped elastic sealing member 210 made of a material such as fluoro rubber (FKM), and having high fuel permeation resistance is attached therein. The resin composite hose 200 is fitted on the mating pipe 206 so as to elastically contact an inner surface of the elastic sealing member 210 with the mating pipe 206.
Meanwhile, reference numeral 212 indicates a bulge portion bulging annularly in a radially outward direction on a leading end portion of the mating pipe 206, reference numeral 214 indicates a hose clamp for fixing the end portion of the outer rubber layer 202 on the mating pipe 206 by tightening in a diametrically contracting direction an outer peripheral surface of the end portion of the outer rubber layer 202 on which the resin layer 204 is not laminated.
In the resin composite hose 200 shown in FIG. 8, the resin layer 204 is not laminated on an end portion of the resin composite hose 200. Therefore, a great resistance is not exerted by the resin layer 204 when the resin composite hose 200 is fitted on the mating pipe 206, and thereby the resin composite hose 200 can be fitted thereon easily with a small force.
And, in the end portion of the resin composite hose 200, the inner surface of the outer rubber layer 202 having elasticity contacts directly with the mating pipe 206, and a good sealing property can be provided between the mating pipe 206 and a portion of the resin composite hose 200 fitted thereon.
By the way, the fuel hose typically has a predetermined curved shape since the fuel hose has to be arranged so as not to interfere with peripheral parts and components.
A typical rubber hose of such curved shape is produced in a following manner as disclosed in Patent Document 2 below. An elongated and straight tubular rubber hose body is formed by extrusion, and the elongated and straight tubular rubber hose body is cut to a predetermined length to obtain a straight tubular rubber hose body 216 that is not vulcanized (or is semivulcanized). Then, as shown in FIG. 9, the straight tubular rubber hose body 216 is fitted on a mandrel 218 that is made of metal and has a predetermined curved shape to be deformed into a curved shape. Before molding or fitting, a mold release agent is applied to a surface of the mandrel 218. The curved tubular rubber hose body is vulcanized with being fitted on the mandrel 218 by heating for a predetermined time. When vulcanization is completed, the hose 220 of curved shape is removed from the mandrel 218, and washed, thereby the hose 220 of curved shape as a finished product can be obtained.
However, in case of the resin composite hose 200 shown in FIG. 8, such production method cannot be employed. In case of the resin composite hose 200 shown in FIG. 8, first of all, the outer rubber layer 202 is solely formed by injection molding, and the resin layer 204 is formed on the inner surface of the outer rubber layer 202 so as to follow a shape of the inner surface thereof.
For formation of the resin layer 204 so as to follow the shape of the inner surface of the outer rubber layer 202, electrostatic coating means is suitably applied.
The electrostatic coating is applied in such manner that an injection nozzle is inserted inside a hose, specifically inside the outer rubber layer 202, and resin powder is sprayed from the injection nozzle onto an inner surface of the hose, thereby the inner surface of the outer rubber layer 202 is electrostatically coated with the resin powder.
In the electrostatic coating, a resin membrane is formed in such manner that negatively or positively charged resin powder (typically, negatively charged resin powder) is sprayed from the injection nozzle, and the resin powder flies to and is attached to the inner surface of the outer rubber layer 202 as counter electrode (positive electrode) by electrostatic field.
In steps of such an electrostatic coating, in order to form the resin layer 204 with an intended thickness, usually, more than one cycles of electrostatic coating are performed. Specifically, after the resin powder is attached on the inner surface of the outer rubber layer 202, the resin powder is melted by heating and then cooled. Then, another resin powder is attached on the resin powder by further spraying the resin powder thereto by an electrostatic coating and the another resin powder is melted by heating and then cooled. In this manner, the cycle of electrostatic coating is repeated until the resin layer 204 with an intended wall thickness is formed.
In this case, overall production steps are as follows.
First, the outer rubber layer 202 is formed by injection molding. Then, the outer rubber layer 202 is dried, washed in pretreatment process and dried again. Subsequently, resin powder is attached to an inner surface of the outer rubber layer 202 by electrostatic coating. The resin powder thereon is melted by heating and then cooled. After that, a second cycle of the electrostatic coating (attaching by electrostatic coating, melting and cooling of resin powder) is performed, and this cycle (attaching by electrostatic coating, melting and cooling of resin powder) is repeated to obtain the resin layer 204 with the intended wall-thickness. After the resin layer 204 is completed, a ring-shaped elastic sealing member 210 having fuel permeation resistance is inserted through an axial end of the outer rubber layer 202 to be placed in a predetermined position.
As stated above, a number of steps are required for producing the resin composite hose 200 shown in FIG. 8, and therefore, production cost of the resin composite hose 200 is necessarily increased.
Although the above are described with reference to a fuel hose as an example. The similar problems arc anticipated in common to any resin composite hose including a resin layer that defines an inner surface layer on inner side of an outer rubber layer in order to prevent permeation of a transported fluid and serves as a barrier layer having a permeation resistance to the transported fluid.
Accordingly, the inventor of the present invention devised a resin composite hose of a multilayer construction in which an inner rubber layer is further laminated on an inner side of a resin layer as an inner surface layer.
The resin composite hose of the multilayer construction can be provided with permeation resistance (barrier property) to a transported fluid by the resin layer. Further, the inner rubber layer that defines an inner surface of the resin composite hose is elastically deformed when the resin composite hose is fitted on a mating pipe, thereby allows a worker to easily fit the resin composite hose on the mating pipe with a small force, namely to easily connect the resin composite hose to the mating pipe with a small force.
And, since the resin composite hose is connected to the mating pipe so as to elastically contact the inner rubber layer with the mating pipe, a good sealing property can be provided between the mating pipe and a portion of the resin composite hose connected thereto.
And, in the resin composite hose of the multilayer construction, since the resin layer can be formed to an axial edge of the hose, an expensive ring-shaped sealing member 210 having high permeation resistance to a transported fluid as shown in FIG. 8 can be omitted.
In addition, in the resin composite hose of the multilayer construction, since the resin layer can be formed to the axial edge of the hose, it becomes possible to produce the resin composite hose that has a curved shape in the same production method as shown in FIG. 9.
Specifically, a straight tubular hose body is formed with a multilayer construction by successively laminating the inner rubber layer, the resin layer and the outer rubber layer on one another by extrusion. The straight tubular hose body is unvulcanized or semivulcanized. Then, the straight tubular hose body is fitted on a mandrel that has a predetermined curved shape to be deformed, the curved tubular hose body with being fitted on the mandrel is vulcanized by heating, and thereby a resin composite hose of curved shape can be obtained.
In this production method, it becomes possible to produce a resin composite hose at much lower cost than before.
However, the inventors test-produced a resin composite hose of curved shape in this manner, and found that the following problem was caused.
FIG. 10 illustrates this problem concretely.
An elongated tubular hose body is formed by extrusion and cut to a predetermined length whereby a tubular hose body of straight shape indicated at reference numeral 222 in FIG. 10A is obtained. The tubular hose body 222 is unvulcanized (or is semivulcanized) and has a multilayer construction comprising an outer rubber layer 202, a resin layer 204 and an inner rubber layer 224 that defines an inner surface of the tubular hose body 222.
When the tubular hose body 222 is fitted on a mandrel 218 having a curved shape, the resin layer 204 exhibits wave-shaped deformation behavior on inner side of a curved portion of the hose body 222, with the consequence that the outer rubber layer 202 also exhibits similar wave-shaped deformation behavior.
The reason for creation of such wave-shaped deformation is estimated as follows.
When the tubular hose body 222 is fitted on the mandrel 218, on an outer side of the curved portion, a pull-force in an axial direction is exerted on the tubular hose body 222, and the tubular body 222 tends to be elongated in the axial direction (axial direction of the hose) while decreasing in wall thickness on the outer side thereof.
On the other hand, on an inner side of the curved portion, an axial compression force is exerted on the tubular hose body 222, and the tubular hose body 222 tends to be forcibly contracted in the axial direction while slightly increasing in wall thickness.
When a hose does not include the resin layer 204 and comprises a rubber layer alone (or a rubber layer and a reinforcing layer), the hose can comply with deformation by pull-out force and deformation under compression, namely, the tubular hose body 222 can be deformed so as to follow the curved shape of the mandrel 218 sufficiently without creating wave-shaped deformation as stated above.
However, in a resin composite hose having the resin layer 204, the resin layer 204 cannot be deformed so as to follow the curved shape of the mandrel 218 favorably, in particular, on the inner side of the curved portion of the resin layer 204, an excess length or loosening is created due to dimensional contraction caused by compression in the axial direction, slack in the axial direction is created thereon, and as a result, wave-shaped deformation is created as shown in FIG. 10B.
[Patent Document 1] JP-A, 2002-54779
[Patent Document 2] JP-A, 11-90993
Under the foregoing circumstances, it is an object of the present invention to provide a resin composite hose that can prevent wave-shaped deformation behavior in a resin layer and has an excellent permeation resistance to a transported fluid, and to provide a method for producing the same.